Comparison of methods for deriving atomic charges from the electrostatic potential and moments

Abstract

Four methods for deriving partial atomic charges from the quantum chemical electrostatic potential (CHELP, CHELPG, Merz-Kollman, and RESP) have been compared and critically evaluated. It is shown the charges strongly depend on how and where the potential points are selected. Two alternative methods are suggested to avoid the arbitrariness in the point-selection schemes and Van der Waals exclusion radii: CHELP-BOW, which also estimate the charges from the electrostatic potential, but with potential points that are Boltzmann-weighted after their occurrence in actual simulations using the energy function of the program in which the charges will be used, and CHELMO, which estimates the charges directly from the electrostatic multipole moments. Different criteria for the quality of the charges are discussed. The CHELMO method gives the best multipole moments for small and medium-sized polar systems, whereas the CHELP-BOW charges reproduce best the total interaction energy in actual simulations. Among the standard methods, the Merz-Kollman charges give the best moments and potentials, but they show an appreciable dependence on the orientation of the molecule.We have also examined the recent warning that charges derived by a least-squares fit to the electrostatic potential normally are not statistically valid. It is shown that no rank-deficiency problems are encountered for molecules with up to 84 atoms if the least-squares fit is performed using pseudoinverses calculated by singular value decomposition and if constraints are treated by elimination.

Tuning of the anion–π interaction

“…We have used the Merz-Kollman scheme for deriving atomic charges and studying charge transfer effects at the same level of theory. It has been reported that this method provides high-quality charges [66].…”

“…This method for deriving atomic charges is expected to give good quality charges [66]. To study the relationship between charge transfer and cooperativity effects, the variation of the anion charge in multicomponent systems 11-28 with respect to the binary anion-p complexes 2-4 is summarized in Table 3 (DQ MK values).…”

Structure-based simulation of linear optical spectra of the CP43 core antenna of photosystem II

“…Geometry optimization of methyl-Chl a is performed with the program Jaguar 5.5 (Schrödinger, L.L.C., Portland, OR, 1991 applying density functional theory (DFT) with the B3LYP exchange correlation (XC) functional and a 6-31G** basis set. Atomic partial charges are obtained as described earlier (Madjet et al 2006) by fitting the electrostatic potential (ESP) using CHELP-BOW (Sigfridsson and Ryde 1998). Excited states of Chl a are calculated by using the program QChem (Kong et al 2000) applying time-dependent (TD)-DFT in the Tamm-Dancoff approximation (Hirata and Head-Gordon 1999) with a 6-31G* basis set and the B65LYP XC-functional defined in earlier work Madjet et al 2009).…”

Atomic charges from IR intensity parameters: theory, implementation and application

“…or are based on the fitting of the molecular electrostatic potentials (ESP charges: MK [14,15], Chelp [16], Chelpg [17], etc.). Many papers compared the results obtained adopting different schemes, underlining the strength and the weakness of each of them [12,[18][19][20][21][22][23]. The charges obtained according to the methods mentioned above share an intrinsic and unavoidable weakness, since they cannot be directly related to any experimentally measurable property.…”